The invention concerns a method for operating an optical sensor for measuring a physical quantity, as well as the corresponding sensor.
In general, one must define a so-called scale value for measurement devices with which a physical parameter is being measured and which operate pursuant to a calibration certificate. The scale value corresponds to the smallest indicated dimensional unit and is used to define the measurement accuracy. The measurement results may only be indicated in multiples of the scale value. By definition, scale values should only be selected in steps of 1, 2 and 5 times 10n (n is an integer). The definition is mandated by national authorities, for example, in Germany, by the Physikalisch Technische Bundesanstalt, which follow the recommendations of the OIML (International Organization of Legal Metrology).
Each calibrated measurement device has one of these scale values and is suitable for applications with a measurement accuracy corresponding to that scale value.
A problem occurs when the measurement accuracy cannot be constant because it is influenced by external conditions. For example, such a situation is encountered when making automatic length or volume measurements with an optoelectronic sensor, such as a laser scanner, of goods being transported by a conveyor. The length measured in the transport direction by a stationary sensor depends on the transport speed. Upon change in that speed, it might become necessary to employ a different sensor calibrated with a different scale value. Thus, the measurement layout at the conveyor either has a limited range of application or it must have several sensors with different scale values, which is correspondingly expensive and cumbersome.